1. Field of the Invention
The present invention relates to a valve timing control device,for modifying the-opening and closing timing of the intake and exhaust valves in an internal-combustion engine (hereafter, ref erred as an engine) according to any operating condition.
2. Description of the Prior Art
Conventional valve timing control devices of various structures,are proposed as disclosed in JP-A-1998/159519, JP-A1998/159520 and JP-A-1999/294120, for example.
FIG. 1 is a lateral cross sectional view of an internal construction of the) conventional vane-type valve timing control device. FIG. 2 is a longitudinal cross sectional view taken along lines A-A of FIG. 1. FIG. 3A and FIG. 3B are enlarged cross sectional views of a lock member in the valve timing control device of FIG. 2, FIG. 3A showing a locked state, and FIG. 3B showing a released state. In the drawings, reference numeral 1 denotes a pulley which connects with, a crankshaft (not shown) of the engine through chains (not shown) to rotate in synchronization with the crankshaft (not shown). 2 denotes a housing fitted to the pulley 1 and having a bearing part 2a with respect to an intake or exhaust camshaft (hereafter, referred as a camshaft) 3. 4 denotes a case having a plurality of shoes 4a, the respective shoes 4a projecting from an inside of the case 4 to constitute a plurality of hydraulic pressure chambers defined between the shoes 4a. 5 denotes a cover of covering the hydraulic pressure chambers of the case 4. The housing 2, the case 4 and the cover 5 are connected, integrally to each other by a threaded member 6 such as a bolt and soon. Here, the pulley 1, the housing 2, the case 4 and the Cover 5 constitute a first, rotor.
A rotor (second rotor) 9 is fixed integrally to an one end 3a of the camshaft 3 by a threaded member 8 such as a bolt and so on through a washer 9. The rotor 7 is arranged rotatably in the first rotor. A plurality of vanes 7a are arranged at an outer circumferential portion of the rotor 7, dividing the hydraulic pressure chambers into an advance side hydraulic pressure chamber 10 and a retardation side hydraulic pressure chamber 11. A first oil passage 12 and a second oil passage 13 are arranged in the camshaft 3. The first oil passage 12 supplies hydraulic pressure to and discharges hydraulic pressure from the advance side hydraulic pressure chamber 10, and the second oil passage 13 supplies hydraulic pressure to and discharges hydraulic pressure from the retardation side hydraulic pressure chamber 11. Moreover, seal means 14 are arranged on both of front ends of the shoes 4a of the case 4 and the vanes 7a of the rotor 7, respectively. The respective seal means 14 prevent leakage of oil between the both of the hydraulic pressure chamber 10 and 11. The seal means 14 includes a seal member 14a of sliding on an inner wall face of the hydraulic pressure chamber 10 or 11 and a plate spring 14b of biasing the seal member 14a toward the inner wall face.
A lock pin 15 having a cylindrical shape is arranged at the housing 2 constituting the first rotor above and restricts relative rotation of the first rotor and the second rotor. Since hydraulic pressure in the valve timing control device is reduced on starting the engine, the rotor 7 acting as the second rotor vibrates in the rotational direction by a cam load applied to a cam (not shown) integrated with the camshaft 3. In this way, since the first and second rotors undergo repetitive contact and separation as a result of the vibration, beat noise (abnormal noise) necessarily results. The lock pin 15 prevents the occurrence of beat noise (abnormal noise). Therefore, the lock pin 15 is biased by a biasing member 17 such as a coil spring toward the second rotor and thus allows the engagement with an engagement hole will be explained hereafter. The biasing member 17 is arranged between a rear wall of a backward pressure chamber 16 and the lock pin 15. A discharge hole 18, which discharges a backward pressure of the lock pin 15, is formed in the backward pressure chamber 16.
On the other hand, an engagement hole 19, which allows insertion of the lock pin 15, is formed at the vane 7a of the rotor 7 acting as the second rotor The engagement hole 19 communicates with a valve 21 through a hydraulic pressure supply passage 20 of supplying a release hydraulic pressure for releasing engagement (hereafter, referred as lock) of the lock pin 15. The valve 21 communicates with both the advance side hydraulic pressure chamber 10 and the retardation side hydraulic pressure chamber 11, and is a member for selecting the higher hydraulic pressure from the above chambers in order to supply the selected pressure to the hydraulic pressure supply passage 20.
Next, a release operation will be explain.
In a release operation, hydraulic pressure is supplied from an oil pump (not shown) to the engagement hole 19 through the advance side hydraulic pressure chamber 10 or the retardation side hydraulic pressure chamber 11, the valve 21 and the hydraulic pressure supply passage 20. In this way, the hydraulic pressure presses the lock pin 15 against the biasing force of the biasing member 17 to move the lock pin 15 back in the backward pressure chamber 16. Here, backward pressure of the lock pin 15 is discharged from the discharge hole 18 to the outside of the valve timing control device. Since an area (an area determined by a diameter D of the lock pin 15 as shown in FIG. 3A) subjected to hydraulic pressure is constant from a locked state of the lock pin 15 to the end of a released state, discharge of the backward pressure is also constant. When a front end of the lock pin 15 is released from the engagement hole 19 and is accommodated in the backward pressure chamber 16, the lock of the lock pin 15 is released to allow free rotation between the first and second rotors.
It is noted that when the engine is stopped, oil in the advance side hydraulic pressure chamber 10 and the retardation side hydraulic pressure chamber 11 moves downwardly to an oil-pan (not shown) through the first and second oil passages 12 and 13 and so on. Therefore, air accumulates in pipe arrangement such as the respective hydraulic pressure chambers and the respective oil passages. In this state, when the engine is restarted, a hydraulic pressure rises by the oil pump (not shown) and simultaneously air accumulated in the pipe arrangement is discharged at once. Thus, the air-mixing oil is applied in the valve timing control device to release instantly the lock pin 15 from the engagement hole 19.
However, the following problems result from the above structure for a conventional valve timing control device.
When the air-mixing oil releases the lock on starting the engine, the hydraulic pressure in the advance side hydraulic pressure chamber 10 and the retardation side hydraulic pressure chamber 11 cannot absorb the cam load described above because of air mixing oil. Since the first and second rotors repeat contact and separation therebetween, beat noise (abnormal noise) necessarily results.
Accordingly, it is an object of the present invention to provide a valve timing control device, which prevents the occurrence of beat noise (abnormal noise) in a release operation resulting from the air-mixing oil on starting the engine.
In order to achieve the object of the present invention, a valve timing control device comprises a first rotor rotating in synchronization with a crankshaft of an internal combustion engine; a second rotor fixed on an end of an intake camshaft or an exhaust camshaft of the internal combustion engine and rotatably arranged in the first rotor; a lock member locking the first and second rotors at a required angle which any one of the rotors forms with the other; a backward pressure chamber arranged at any one of the first and second rotors, the backward pressure chamber allowing accommodation of the lock member and a biasing member biasing the lock member and having a discharge hole for discharging the backward of the lock member to the outside; an engagement hole arranged at the other rotor, the engagement hole allowing insertion of the lock member and having a hydraulic pressure supply passage for supplying a hydraulic pressure used for releasing lock due to the lock member and a variable throttle mechanism arranged in the backward pressure chamber, the variable throttle mechanism throttling an opening area of the discharge hole in the backward pressure chamber on releasing the lock due to the lock member and controlling the opening area of the discharge hole at the maximum on locking due to the lock member. In this way, since the opening area of the discharge hole can be throttled on releasing the lock due to the lock member, a discharge speed of the backward pressure can delay considerably as compared with the conventional device. Thus, a backward speed of the lock member and a speed of releasing the lock can be also delayed. Moreover, with a state of rising a hydraulic pressure on starting the engine, a release operation due to the lock member cannot be performed promptly. After the hydraulic pressure sufficient to control the valve timing control device is applied thereto, the lock member can be released and thus can prevent beat noise (abnormal noise) which occurs in the conventional example. Since a closing of the discharge hole due to the variable throttle mechanism can be released on locking the lock due to the lock member, the engagement due to the lock member can be performed at the same speed as the conventional device.
The variable throttle mechanism may include a sliding member having a perforation hole formed inside thereof, the sliding member closing the discharge hole on releasing the lock due to the lock member and opening the discharge hole on locking due to the lock member. In this way, since the sliding member can be slid in response to the sliding motion of the lock member, the discharge hole can be closed on releasing the lock due to the lock member and can be opened on locking due to the lock member.
The sliding member may slide in parallel with the sliding axis of the lock member to close the discharge hole on releasing the lock due to the lock member and may slide in parallel with the sliding axis of the lock member to open the discharge hole on locking due to the lock member. In this way, since the sliding member can be slid in response to the sliding motion of the lock member, the discharge hole can be closed on releasing the lock due to the lock member and can be opened on locking due to the lock member.
The variable throttle mechanism may close the discharge hole continuously and variably. In this way, since the opening area of the discharge hole on releasing the lock due to the lock member can be throttled continuously and variably, a releasing speed can be changed continuously.
The variable throttle mechanism may have a biasing member for biasing the sliding member in a direction of opening the discharge hole on locking the lock due to the lock member. In this way, since the sliding member, which throttles the opening area of the discharge hole on locking due to the lock member until now, can be slid in a direction of controlling the opening area of the discharge hole at the maximum, the engagement due to the lock member can be performed at the same speed as the conventional device.
The variable throttle mechanism may include a throttle rod integrated with the lock member, the throttle rod closing the discharge hole on releasing the lock due to the lock member and opening the discharge hole on locking due to the lock member. In this way, with the device, the discharge hole can be closed on releasing the lock due to the lock member and can be opened on locking. Moreover, since the number of parts of the device can be reduced, it is possible to reduce manufacturing costs and facilitate assembly.
The throttle rod may slide coaxially on the sliding axis of the lock member to close the discharge hole on releasing the lock due to the lock member and may slide coaxially on the sliding axis of the lock member to open the discharge hole on locking due to the lock member. In this way, the discharge hole can be closed effectively on releasing the lock due to the lock member and opened effectively on locking.
The variable throttle mechanism may close the discharge hole in a stepwise manner. In this way, the opening area of the discharge hole can be throttled in a stepwise manner on releasing the lock due to the lock member, the releasing speed can be changed in a stepwise manner.